Weep holes are small openings built into parts of a building to let water drain out and to support airflow. They are most common in masonry walls, retaining walls, window and door frames, and some cladding systems. In simple terms, a weep hole is a controlled exit point for moisture that would otherwise stay trapped.
Homes and buildings deal with moisture all the time. Rain, wind-driven spray, condensation, and even small leaks can introduce water into places you can’t easily see. Weep holes help manage that moisture by allowing drainage and reducing pressure build-up.
Why weep holes exist
1) Drainage
Walls and frames can collect water. This is normal. Brickwork can absorb moisture. Water can also enter through tiny gaps, especially during heavy rain or strong wind. In cavity walls, moisture can run down the inner face of the outer wall layer. A weep hole gives that moisture a way out.
2) Ventilation
Weep holes can also help the wall system “breathe”. Ventilation reduces trapped humidity. That matters because moisture left in a cavity can contribute to damp conditions over time.
3) Pressure relief
In retaining walls, weep holes relieve water pressure. Without pressure relief, a retaining wall can crack, bow, or fail. Weep holes are a practical part of safe drainage design.
Where you’ll find weep holes
Weep holes in brick and masonry walls
In cavity brick walls, weep holes are typically placed near the bottom of the wall. They often appear above the damp-proof course (DPC) or near flashing points. Their job is to release moisture that collects inside the cavity.
Weep holes above windows and doors
You may see weep openings above window frames where lintels and flashing direct water outward. Water that lands behind the outer layer needs a route to escape.
Weep holes in retaining walls
These openings are often visible as small pipes or gaps through the wall. Their purpose is to drain groundwater and reduce hydrostatic pressure.
Weep holes in aluminium and uPVC window frames
Many window systems include drainage channels and small outlet openings. These are also called weep holes. They allow water that enters the frame system to drain to the outside.
Types of weep holes
Open head-joint weep holes
Rope or wick weeps
Plastic weep vents / weep hole vents
Pipe weeps (retaining walls)
How weep holes work in a cavity wall
A cavity wall typically has:
An outer leaf (often brick)
A cavity (a gap between layers)
An inner leaf (brick or blockwork)
Wall ties that connect the two leaves
DPC and flashing to direct water
When water enters the outer leaf or gets behind it, it can run downward inside the cavity. Flashing helps guide it toward the outside. Weep holes provide the exit point so water can leave the system rather than pooling inside.
What happens when weep holes are missing or blocked?
When a weep opening is missing, too few, or blocked, moisture may stay trapped. That can contribute to problems like:
Damp patches on interior walls
Paint bubbling or peeling
Efflorescence (white salt marks on brickwork)
Musty odours and higher humidity
Increased likelihood of mould in affected areas
Cracks that worsen when moisture and temperature changes repeat
Water staining around windows or below lintels
In retaining walls, blocked weep holes can be more serious because pressure can build behind the wall.
Should you cover weep holes?
Weep holes should not be sealed shut. They exist for drainage and ventilation. If you block them completely, you may stop water from escaping.
That said, many homeowners want to reduce what can enter through an open gap. An uncovered opening can allow:
Insects and crawling pests
Wind-blown debris
Splashing rain during storms
Airborne embers in high-risk conditions
A good approach is using a purpose-made weep hole cover or weep hole screen that still supports airflow and drainage while adding a protective barrier. The key is to avoid fully sealing the opening.
How many weep holes should there be?
This depends on the wall design, local building practices, and where flashing is installed. Weep holes are commonly spaced at intervals along the wall, especially above openings like windows and doors, and near the base of cavity walls.
If you’re unsure, it’s best to get advice from a qualified builder or building professional, especially if you’re dealing with ongoing damp.
Quick checklist: spotting weep hole issues
Use this simple list as a guide:
Can you see weep openings at the base of the wall or above windows?
Are the openings blocked by mortar, paint, soil, or paving?
Is there visible damp, staining, or bubbling paint indoors?
Are there signs of pests around openings?
Do you see salt marks on brickwork after rain?
If you answered “yes” to any of these, it may be worth checking the drainage path and ensuring the openings can do their job.
Frequently asked questions
They are designed to let water out, but during extreme wind-driven rain, splashing can occur. That’s why many people choose a protective vent or cover that reduces direct entry while keeping drainage working.
It’s not recommended. Sealing them can trap water in the cavity or frame system. If you’re trying to stop pests, use a proper weep hole screen or vent instead of sealing the hole shut.
No. They are used in many building systems, including windows, doors, retaining walls, and cladding. The goal is always moisture management.
If you see damp problems after rain, or you can’t see any clear opening where one should exist, they may be blocked. Sometimes paint or mortar closes them over.
Yes. Moisture still needs a path to escape. Good building design manages water rather than pretending it won’t happen.
Summary
Weep holes are a simple but important part of building moisture control. They help with drainage, ventilation, and pressure relief. When they are missing or blocked, moisture problems can build up over time. The best practice is to keep weep holes functional, while using the right products if you want added protection from pests, debris, splash, or embers.
